The object of the proposed research program is to study the role of cysteine residues in the different facets of hemoglobin structure and function (tetramer formation, oxygen binding, etc). Hemoglobins A, F, and S have been chosen because of the differences which exist in the primary structure of the Beta-like subunit of these molecules. The cysteine residues on individual hemoglobin subunits will be modified noncovalently by reaction with p-mercuribenzoate and covalently by reaction with iodoacetamide. Modified hemoglobin derivatives will be prepared by mixing one derivatized subunit with opposite normal subunits. Products which resemble the native hemoglobin chromatographically and electrophoretically will be isolated and their equilibrium properties during oxygen binding will be compared with respect to differences in primary sequence of the Beta-like subunit. In addition, the cysteine residues will also be used as sites for spin-label probes which will be used to monitor, by electron spin resonance, structural changes which take place within the different hemoglobin molecules during reversible oxygen binding. The information obtained from these studies should help elucidate the nature of the structural differences between these three hemoglobins and, therefore, provide further information concerning their functional differences, such as the involvement of hemoglobin S in sickle cell anemia.